Water Adsorption on Kaolinite Surfaces Containing Trenches

Recent laboratory Studies of water adsorption on kaolinite at 296 K, and at relative humidity (RH) values relevant for the atmosphere, have reported coverages ranging LIP to tens of monolayers. In contrast, recent simulations have suggested that atomistically smooth kaolinite surfaces uptake only monolayers (some slightly overgrown) at similar RH values. In an effort to possibly explain the laboratory data, we have performed water adsorption calculations oil kaolinite surfaces containing trenchlike structures using the grand canonical Monte Carlo simulation method at 298 K. The results obtained show that the granularity of the surfaces can play a major role in the adsorption of multiple layers of water. For all trenches considered, multilayers of water were observed over a large range of RH. The narrowest trench investigated remained filled with water even in the very low RH regime (<= 0.0003%). Increasing the trench width resulted in partial or complete trench filling depending oil the RH value, with large water mounds growing oil the step edges. This strong affinity for water is explained by very attractive water-lattice interactions inside the trenches, especially near the walls. Our calculations Suggest that water adsorption in trenches, and possibly in other similar defects, can offer an explanation of the experimental results.